光致折变晶体中相位光栅的相位移动的物理作用

Physical effect of phase shift of phase grating in photorefractive crystals

在光致折变晶体(如SBN,BaTiO_3等)中发生两波混频及能量耦合是由于晶体干涉场内产生了相对于干涉场有相位移动的折射率光栅(相位光栅),这已被实验和理论证实。如果仅有两波混频产生的相位光栅,而此光栅相对于干涉场并无相位移动,或相位移动量较小(不足π/2),此时不会发生波能量耦合或耦合极微弱。1981年A.Yariv用耦合波方程从数学上解决了这个问题。

It is proved that there exists π/2 phase difference between the transmitted beam and the diffracted (or reflected) beam of one incident wave when they leave a thick grating (or another beam splitter). It is the phase difference that makes energy coupling between input-beam possible when there is the phase shift between phase grating and the inter ference pattern of the incident wave in the photorefractive crystal, and the diffraction efficiency of phase grating and modulation amplitude of photorefractive index are calculated based on the theory.